Thermoelectric (TE) generators enable the direct and reversible conversion between heat and electricity, providing applications in both refrigeration and power generation. In the last decade, several TE materials with relatively high figures of merit (zT) have been reported in the low‐ and high‐temperature regimes. However, there is an urgent demand for high‐performance TE materials working in the mid‐temperature range (400–700 K). Herein, p‐type AgSbTe2 materials stabilized with S and Se co‐doping are demonstrated to exhibit an outstanding maximum figure of merit (zTmax) of 2.3 at 673 K and an average figure of merit (zTave) of 1.59 over the wide temperature range of 300–673 K. This exceptional performance arises from an enhanced carrier density resulting from a higher concentration of silver vacancies, a vastly improved Seebeck coefficient enabled by the flattening of the valence band maximum and the inhibited formation of n‐type Ag2Te, and ahighly improved stability beyond 673 K. The optimized material is used to fabricate a single‐leg device with efficiencies up to 13.3% and a unicouple TE device reaching energy conversion efficiencies up to 12.3% at a temperature difference of 370 K. These results highlight an effective strategy to engineer high‐performance TE material in the mid‐temperature range.

In the present work, we detail af ast and simple solution-based method to synthesize hexagonal SnSe 2 nanoplates (NPLs) and their use to produce crystallographically textured SnSe 2 nanomaterials.W ea lso demonstrate that the same strategy can be used to produce orthorhombic SnSe nanostructures and nanomaterials.N PLs are grown through as crew dislocation-driven mechanism. This mechanism typically results in pyramidal structures,b ut we demonstrate here that the growth from multiple dislocations results in flower-like structures.C rystallographically textured SnSe 2 bulk nanomaterials obtained from the hot pressing of these SnSe 2 structures displayhighly anisotropic charge and heat transport properties and thermoelectric (TE) figures of merit limited by relatively low electrical conductivities.T oimprove this parameter,SnSe 2 NPLs are blended here with metal nanoparticles.The electrical conductivities of the blends are significantly improved with respect to bare SnSe 2 NPLs,w hat translates into at hree-fold increase of the TE Figure of merit, reaching unprecedented ZT values up to 0.65.The use of molecular precursors to produce inorganic nanomaterials in the form of nanoparticles,t hin films, supported nanostructures or self-standing porous or dense nanomaterials is potentially advantageous in terms of reducing fabrication costs and improving performances.I nt his direction, the amine-dithiol system has been reported as av ersatile solvent to prepare molecular precursors from the dissolution at ambient conditions of metal chalcogenides, pure metals and metal oxides,a mong others. [1] Tw odimensional (2D) materials have attracted increasing attention in the past decade.T he structure of these materials is formed by atomically thin layers that display strong covalent in-plane bonding and weak layer-to-layer bonding. This type of structure results in extraordinary and at the same time highly anisotropic physical, electronic and optical properties.Inparticular, charge and heat transport properties are especially affected by the strong lattice asymmetry,a nd much higher thermal and electrical conductivities are measured in-plane than cross-plane.O wing to these highly anisotropic properties,t op roduce bulk 2D nanomaterials with aproper crystallographic texture is necessary to optimize their performance in most applications.H owever,t oc ontrol the crystallographic texture of materials produced by bottomup procedures and/or solution-based approaches is not straightforward.Ap articularly interesting 2D material family is that of metal chalcogenides,o wing to their good chemical stability and semiconducting characteristics.2 Dm etal chalcogenides are used in numerous applications in av ariety of fields, including energy conversion and storage, [2] flexible electronics [3] and medical diagnosis. [4] Among them, tin chalcogenides are especially interesting materials for energy conversion. [5] In particular,p -type SnSe single crystals have shown unprecedentedly high thermoelectric (TE) figures of merit:Z T= 2.6 at 92...

Properly designed nanocomposites allow improving thermoelectric performance by several mechanism, including phonon scattering, modulation doping and energy filtering, while additionally promoting mechanical properties over those of crystalline materials. Here, a...

To achieve optimal thermoelectric performance, it is crucial to manipulate the scattering processes within materials to decouple the transport of phonons and electrons. In half-Heusler (hH) compounds, selective defect reduction can significantly improve performance due to the weak electron-acoustic phonon interaction. This study utilized Sb-pressure controlled annealing process to modulate the microstructure and point defects of Nb0.55Ta0.40Ti0.05FeSb compound, resulting in a 100% increase in carrier mobility and a maximum power factor of 78 µW cm−1 K−2, approaching the theoretical prediction for NbFeSb single crystal. This approach yielded the highest average zT of ~0.86 among hH in the temperature range of 300-873 K. The use of this material led to a 210% enhancement in cooling power density compared to Bi2Te3-based devices and a conversion efficiency of 12%. These results demonstrate a promising strategy for optimizing hH materials for near-room-temperature thermoelectric applications.

Composite materials offer numerous advantages in a wide range of applications, including thermoelectrics. Here, semiconductor−metal composites are produced by just blending nanoparticles of a sulfide semiconductor obtained in aqueous solution and at room temperature with a metallic Cu powder. The obtained blend is annealed in a reducing atmosphere and afterward consolidated into dense polycrystalline pellets through spark plasma sintering (SPS). We observe that, during the annealing process, the presence of metallic copper activates a partial reduction of the PbS, resulting in the formation of PbS−Pb− Cu x S composites. The presence of metallic lead during the SPS process habilitates the liquid-phase sintering of the composite. Besides, by comparing the transport properties of PbS, the PbS−Pb−Cu x S composites, and PbS−Cu x S composites obtained by blending PbS and Cu x S nanoparticles, we demonstrate that the presence of metallic lead decisively contributes to a strong increase of the charge carrier concentration through spillover of charge carriers enabled by the low work function of lead. The increase in charge carrier concentration translates into much higher electrical conductivities and moderately lower Seebeck coefficients. These properties translate into power factors up to 2.1 mW m −1 K −2 at ambient temperature, well above those of PbS and PbS + Cu x S. Additionally, the presence of multiple phases in the final composite results in a notable decrease in the lattice thermal conductivity. Overall, the introduction of metallic copper in the initial blend results in a significant improvement of the thermoelectric performance of PbS, reaching a dimensionless thermoelectric figure of merit ZT = 1.1 at 750 K, which represents about a 400% increase over bare PbS. Besides, an average ZT ave = 0.72 in the temperature range 320−773 K is demonstrated.

The direct, solid state, and reversible conversion between heat and electricity using thermoelectric devices finds numerous potential uses, especially around room temperature. However, the relatively high material processing cost limits their real applications. Silver selenide (Ag 2 Se) is one of the very few n-type thermoelectric (TE) materials for room-temperature applications. Herein, we report a room temperature, fast, and aqueous-phase synthesis approach to produce Ag 2 Se, which can be extended to other metal chalcogenides. These materials reach TE figures of merit (zT) of up to 0.76 at 380 K. To improve these values, bismuth sulfide (Bi 2 S 3 ) particles also prepared in an aqueous solution are incorporated into the Ag 2 Se matrix. In this way, a series of Ag 2 Se/Bi 2 S 3 composites with Bi 2 S 3 wt % of 0.5, 1.0, and 1.5 are prepared by solution blending and hot-press sintering. The presence of Bi 2 S 3 significantly improves the Seebeck coefficient and power factor while at the same time decreasing the thermal conductivity with no apparent drop in electrical conductivity. Thus, a maximum zT value of 0.96 is achieved in the composites with 1.0 wt % Bi 2 S 3 at 370 K. Furthermore, a high average zT value (zT ave ) of 0.93 in the 300−390 K range is demonstrated.

AgSbSe 2 is a promising thermoelectric (TE) ptype material for applications in the middle-temperature range. AgSbSe 2 is characterized by relatively low thermal conductivities and high Seebeck coefficients, but its main limitation is moderate electrical conductivity. Herein, we detail an efficient and scalable hot-injection synthesis route to produce AgSbSe 2 nanocrystals (NCs). To increase the carrier concentration and improve the electrical conductivity, these NCs are doped with Sn 2+ on Sb 3+ sites. Upon processing, the Sn 2+ chemical state is conserved using a reducing NaBH 4 solution to displace the organic ligand and anneal the material under a forming gas flow. The TE properties of the dense materials obtained from the consolidation of the NCs using a hot pressing are then characterized. The presence of Sn 2+ ions replacing Sb 3+ significantly increases the charge carrier concentration and, consequently, the electrical conductivity. Opportunely, the measured Seebeck coefficient varied within a small range upon Sn doping. The excellent performance obtained when Sn 2+ ions are prevented from oxidation is rationalized by modeling the system. Calculated band structures disclosed that Sn doping induces convergence of the AgSbSe 2 valence bands, accounting for an enhanced electronic effective mass. The dramatically enhanced carrier transport leads to a maximized power factor for AgSb 0.98 Sn 0.02 Se 2 of 0.63 mW m −1 K −2 at 640 K. Thermally, phonon scattering is significantly enhanced in the NC-based materials, yielding an ultralow thermal conductivity of 0.3 W mK −1 at 666 K. Overall, a record-high figure of merit (zT) is obtained at 666 K for AgSb 0.98 Sn 0.02 Se 2 at zT = 1.37, well above the values obtained for undoped AgSbSe 2 , at zT = 0.58 and state-of-art Pb-and Te-free materials, which makes AgSb 0.98 Sn 0.02 Se 2 an excellent p-type candidate for medium-temperature TE applications.

Cu2–x S and Cu2–x Se have recently been reported as promising thermoelectric (TE) materials for medium-temperature applications. In contrast, Cu2–x Te, another member of the copper chalcogenide family, typically exhibits low Seebeck coefficients that limit its potential to achieve a superior thermoelectric figure of merit, zT, particularly in the low-temperature range where this material could be effective. To address this, we investigated the TE performance of Cu1.5–x Te–Cu2Se nanocomposites by consolidating surface-engineered Cu1.5Te nanocrystals. This surface engineering strategy allows for precise adjustment of Cu/Te ratios and results in a reversible phase transition at around 600 K in Cu1.5–x Te–Cu2Se nanocomposites, as systematically confirmed by in situ high-temperature X-ray diffraction combined with differential scanning calorimetry analysis. The phase transition leads to a conversion from metallic-like to semiconducting-like TE properties. Additionally, a layer of Cu2Se generated around Cu1.5–x Te nanoparticles effectively inhibits Cu1.5–x Te grain growth, minimizing thermal conductivity and decreasing hole concentration. These properties indicate that copper telluride based compounds have a promising thermoelectric potential, translated into a high dimensionless zT of 1.3 at 560 K.